GB2111320A

GB2111320A - Electric tool with integral motor

Info

Publication number: GB2111320A
Application number: GB08228416A
Authority: GB
Inventors: Pierre Raymond Tardieu; Yves H Mulet-Marquis
Original assignee: Kollmorgen Technologies Corp
Current assignee: Kollmorgen Technologies Corp
Priority date: 1981-10-08
Filing date: 1982-10-05
Publication date: 1983-06-29
Also published as: FR2514250B1; IT8249230A0; JPS6058852B2; US4486176A; DE3237197A1; GB2111320B; JPS5875545A; FR2514250A1; CH650661A5; IT1149382B; DE3237197C2

Description

1 GB 2 111 320 A 1

SPECIFICATION

Handpiece with integrated motor The present invention relates to a handpiece with integrated motor for driving tools of small dimensions comprising an outer housing with a rear end part of a diameter sufficient for incorporating the said electric motor, and an intermediary part having a conical part, and a part of reduced diameter which carries means for transferring the rotation of the toolshaft housed in 75 the head part.

Handpieces of the kind described are mainly used in dental surgery. For the drive of the rotating tools several devices such as electric motors and air turbines are known.

Air turbines permit high rotating speeds such as 100 000 rpm and more. The torque of the air turbines at such speeds is, however, rather weak. Besides, such air turbines are very noisy which is a burden for the patient and the practitioner.

Electric motors render a considerable torque at low speeds about up to 40 000 rpm. Therefore, when using such electric motors, they must necessarily comprise a gear train for multiplying the rotation speed. Such gear trains are very easily damaged by overload, and daily lubrication of the bearings is required. Handpieces of conventional design are provided with electric motors with brushes; said brushes are subject to wear and have to be exchanged frequently. The brushes are arranged in the interior part of the motor and their replacement asks for a certain skill.

Furthermore, the motor has to be water-proof for lubricating and water cooling of the tool, a fact 100 that causes the well-known problems always arising when water and electricity are used. Hermetical sealing is especially difficult in the area of the brushes. 40 It is an object of the present invention to avoid 105 the above described disadvantages and to achieve rotation speeds as high as conventionally known for air turbines, combined with the high torque of electric motors. 45 It is a further object of the present invention to provide a reliable electric insulation and, thereby, increase the safety of the operating tool. It is a still further advantage of the present invention that overload is absolutely excluded thus making an automatic device to prevent overload superfluous.

In accordance with the present invention, all these advantages are achieved with a handpiece with integrated tool holder and electric drive motor assembly comprising an outer housing with a rear end part of a diameter sufficient for incorporating the said electric drive assembly, and an intermediary part having a conical section, and a head part 20 having a reduced diameter and forming the housing for the toolholder with toolholder shaft, and a brushless electric motor drive assembly comprising a rotor assembly comprising permanent magnets having the coaxial outer surfaces coated with a layer of electrically conductive metal, said rotor assembly being rotatably mounted and hermetically sealed in a rotor housing made of insulating material; said motor assembly further comprising a stator assembly comprising winding coils of a multiphase field winding embedded in a layer of insulating material; said rotor assembly as well as one or more transmission shaft(s) and the toolholder shaft being provided with magnetic coupling means for transmitting the torque generated by said electric motor assembly to said toolholder without mechanical contact of the coupling means.

The speed of the rotor depends upon the rotational speed of the stator field which depends on the frequency of the supply current. The frequency of the supply current is adjustable with conventional means.

Although the electric motor in correspondence with the present invention is of small dimension, it permits high speeds comparable to those achieved with air turbines. For example, in case the supply current has 2.000 cycles for a bi-polar motor, the speed is 120.000 rpm. The use of magnetic coupling means without mechanical contact avoids mechanical wear and, at the same time, the lubrification problem.

The magnetic coupling means for transmitting the torque from the rotor shaft to the toolholder shaft comprises at least one shaft rotatably mounted in bearings in the center part of the housing and provided on both ends with at least one pair of permanent magnets of small dimensions.

In one embodiment of the present invention, the toolholder is rotatably mounted by means of bearings in the head part of the housing and the toolholder shaft is provided with a first disc of plastic material for transmitting the torque generated by the electric motor, said first disc being provided with small permanent magnets arranged regularly abouts its periphery and embedded in the plastic material.

The magnetic coupling means comprises at least one shaft rotatably mounted in bearings in the center part of the housing, said shaft being provided at the end pointing to the toolholder with a second disc of plastic material provided with small permanent magnets regularly arranged about its periphery and embedded in said plastic material, said second disc forming a magnetic coupling with said first disc mounted on the toolshaft.

The magnetic coupling as described ensures a safe protection against overload, because in case the shaft of the toolholder should be blocked, the outer shaft is still freely rotatable without being damaged. The toolholder shaft and the shaft transmitting the rotation movement may be arranged under an angle of 900 to each other or in parallel or in any angle between 0 and 900.

In the latter case, it is advantageous to provide one of the first and second discs with a conic part on the side facing the other disc.

2 GB 2 111 320 A 2 In a special embodiment of the invention with an angled housing the transmission shaft cooperating with the handpiece also co-operates with a second transmission shaft and is provided ' at its second end co-operating with said second transmission shaft with a third disc of plastic material which is also provided with small permanent magnets arranged regularly about its periphery and embedded in said plastic material.

The second shaft is provided on its one end with small magnets to receive the rotation movement transmitted by the rotor of the motor. At its other end, the second shaft is provided with a fourth disc made of plastic material and with small permanent magnets arranged regularly about its periphery and embedded in said plastic material, co-operating with the magnets of.the third disc thereby providing another magnetic coupling.

Other features and advantages of the present 5 be obvioL.3 fl,om the following inventionw. 85 description taker, In connection with the accompanying drawings.

Fig. 1:s a schematic view of an axial section of one embodiment of the handpiece in accordance with the invention.

Fig. 2 is an enlarged partial view of the magnetic coupling means as used in the handplece in accordance with the invention.

Fig. 3 is a partia.1 view of an axial section of another embodiment in accordance with the invention with an angled housing.

The handpiece of Fig. 1 comprises an outer housing with a rear end part 16 of a diameter sufficient for incorporating the electric motor assembly, and an intermediary part 19 having a conical section, and a head part 20 with reduced diameter which is connected.to the intermediary part 19. The rear part 16 consists of metallic material housing a small brushiess electric motor of the type disclosed in copending patent application No. filed at the same date.

The small electric motor comprises a rotor assembly hermetically sealed in a plastic housing with a capsule 11 and a flange part 12 at its rear end, and a stator assembly comprising winding coils of a multiphase field winding 13 embedded in a layer of insulating material 9 inside of the housing 16. The field winding of the stator 13 may consist of three winding coils. The angular distance between the coils of the field winding is 27r/3 and they are connected to a tri phase electric power supply providing a phase difference between the phases of 27r/3.

The rotor comprises a shaft 4 rotatably mounted in bearings 3 and 3' inside of the plastic 120 housing 10, a tube- like part 5 made of magnetic material and carrying permanent magnets 6 and 6' with opposite poles having coaxial surfaces coated with a layer of electrically conductive metal 8. The rotor housing 10 is provided at its front part with a recessed part 17, forming an axial cylindric cavity 18 facing to the outside.

Portions 7 of the permanent magnets 6 and 6' extend into the sleeves formed inside of said housing 10 by the recessed parts 17 and outside130 of the housing 10 thus providing one part of a magnetic coupling for transmitting the rotor torque to an outside shaft 23 provided with a respective magnetic coupling counter part 21 having two diametrically opposed permanent magnets 22. The shaft 23 is supported by two bearings 24 and 24' in known manner which are arranged inside the center part 19.

At the front end of shaft 23 there is mounted a disc 25 of plastic material provided on its front face with small permanent magnets 26 regularly arranged about its periphery and embedded in the plastic material. The head part 20 of the toolholder comprises toolholder shaft 29 rotatably mounted in bearings 30 and 30', said shaft 29 being provided with a disc 27 made of plastic material having small permanent magnets 28 regularly arranged about its periphery and embedded in the plastic material. The disc 27 is magnetically coupled through permanent magnets 26 and 28 with disc 25 and thereby the torque is transmitted from shaft 23 to shaft 29.

Fig. 2 is a perspective view of the disc 25 and 27 with magnets 26 and 28. For explanatory purposes it is assumed that each disc has two adjacent magnets 26a and 26b and 28a and 28b, respectively. Disc 25 rotates counter-clockwise so that magnet 26a will react with magnet 28a of disc 27 so that disc 27 will start rotating clockwise until magnet 26b will get close to magnet 28b etc. If both discs 25 and 27 have the same diameter and the same number of embedded magnets, they will rotate with the same speed. If so desired, different numbers of magnets maybe used thereby achieving a change in speed of rotation. It is only required that the magnets are arranged in equal distances from each other about the periphery of the discs.

In Fig. 1 and 2 the shafts of discs 25 and 27 are arranged under an angle of 901 to each other, the magnets 26 being on the front surface of disc 25 and co-operating with magnets 28 arranged on the entire periphery of disc 27, thus providing for a minimum distance between the magnet surfaces. The same concept of magnetic coupling can be used with discs having their shafts arranged in parallel or under any desired angle. The arrangement of the embedded magnets should be such that the distance of the surfaces of the magnets on both discs is a minimum, so that the magnets can cooperate with each other. To make sure that the distance between the magnet surfaces is a minimum, it is suggested that, when the shatts are arranged under an angle of other than 900, one of the discs is provided with a conical part for embedding the magnets.

It is a special advantage of the magnetic coupling means of the present invention that, in case the disc 27 is jammed, the disc 25 is freely rotatable without any damage. The magnetic coupling described makes mechanical protection system superfluous.

Fig. 3 shows an embodiment of the invention having an angled housing. In this embodiment, the head part 20 with toolholder 29 is identical 1 3 GB 2 111 320 A 3 with the embodiment shown in Fig. 1. Mounted on toolholder shaft 29 is the disc 27 provided with the small permanent magnets 28 cooperating with the small magnets 26 of disc 25 5 mounted on the front end of transmission shaft 23. The rear end 16 of the housing accommodating the motor, not shown in Fig. 3, is identical with the respective part shown in Fig. 1.

The handpiece shown in Fig. 3 is angled and has an additional shaft 32 for transmitting the torque from the shaft 4 of the electric motor (Fig. 1) to the shaft 23 which drives the toolholder shaft 29. The additional shaft 32 is mounted in bearings 33 and 33' arranged in the intermediary l 5 part 31 of the housing. The shaft 32 has mounted on its rear end (not shown in Fig. 3) the part 21 with magnets 22 of Fig. 1.

The additional shaft 32 is provided at its front end with a plastic disc 34 similar to discs 25 and 27 with a number of small magnets 35 regularly spaced and embedded in its periphery. The disc 34 co-operates with another disc 36 similar to discs 25, 27 and 34 and mounted on the rear end of shaft 23. The discs 34 and 36 being arranged under an angle towards one another, it is advantageous that one of them, e.g., disc 34, has a conical part 38, thus providing for parallel surfaces of magnets on both discs at the locus of minimum distance between said discs.

The handpieces in accordance with the present invention may comprise several angled parts and, in such case, more than two transmission shafts 23 and 32 under an angle towards one another and interacting magnetically. The coupling system between two shafts in series is the same as hereinabove described using discs provided with a number of permanent magnets evenly spaced on their peripheries and embedded in the plastic material of the discs. Thereby, the advantages of 40 the present invention are realized, which comprise the automatic protection from mechanical overload, the almost complete avoidance of wear of the transmission means, the possibility of a lifetime lubrication of the bearings and the simple 45 mode of exchanging the encapsulating rotor.

Claims

1. Handpiece with integrated toolholder and electric drive motor assembly comprising an outer housing with a rear end part 16 of a diameter sufficient for incorporating the said electric drive assembly, and an intermediary part 19 having a conical section, and a headpart 20 having a reduced diameter and forming the housing for the toolholder with toolholder shaft 29; and a brushless electric motor drive assembly comprising a rotor assembly comprising 120 permanent magnets 6, 61 having the coaxial outer surfaces coated with a layer of electrically conductive metal 8, said rotor assembly being rotatably mounted and hermetically sealed in a rotor housing 10 made of insulating material; said 125 motor assembly further comprising a stator assembly comprising winding coils of a multiphase field winding 13 embedded in a layer of insulating material 9; said rotor assembly as well as one or more transmission shaft(s) and the toolholder shaft being provided with magnetic coupling means for transmitting the torque generated by said electric motor assembly to said toolholder without mechanical contact of the coupling means.

2. The handplece of claim 1, wherein the magnetic coupling means comprises at least one pair of permanent magnets of small dimensions mounted at the ends of shaft 23 mounted in bearings 24, 24' in housing part 19.

3. The handpiece of claims 1 or 2, wherein the toolholder shaft 29 is mounted in bearings 30, 301 in head part 20 and wherein said shaft 29 is provided with a disc made of plastic material 27, provided with small permanent magnets which are regularly arranged about the periphery of said disc and embedded in the plastic material.

4. The handplece of claim 3, wherein the magnetic torque transmission means comprises at least a shaft 23, mounted in bearings 24, 241, and wherein said shaft 23 is provided on the end pointing to the toolholder 20 with a disc 25 made of plastic material and provided with small permanent magnets 26 regularly arranged about its periphery and embedded in said plastic material, and wherein said second plastic disc 25 forms a magnetic coupling with said first disc 27 mounted on toolholder shaft 29. jk

5. The handplece of claim 4, wherein the discs and 27 are arranged under an angle of 901 to each other and are located in such way that they form a magnetic coupling for transmitting torque from shaft 23 to toolholder shaft 29.

6. The handpiece of claim 4, wherein discs 25 and 27 as well as the respective shafts are arranged parallel to each other.

7. The handpiece of claim 4, wherein the discs mounted on shaft 23 and shaft 29 are arranged under an angle to each other.

8. The handplece of claim 7, wherein the one or the other of discs 25 and 27 is provided with a conical portion 38 (Fig. 3) thus providing for parallel surfaces of magnets on both discs at the locus of minimum distance between said discs.

9. The handpiece of one or more of cleims 4 to 8, wherein the part 19 of the outer housing is angled, and wherein shaft 23 is provided on both ends with discs provided with small permanent magnets 26 and 37 embedded about the periphery of said discs 25 and 36, with disc 25 with its magnets 26 co-operating with disc 27 with magnets 28 and disc 36 with magnets 37 co-operating with disc 34 having a conical part 38 and magnets 35, said disc being mounted on the one end of shaft 32, and wherein said shaft 32 is provided on its other end with a disc 21 with magnets 22 co-operating with the extended portion of rotor magnets 6, 6' thus forming magnetic couplings between said magnets 6, 6' and disc 21 (Fig. 1) as well as between discs 34 and 36 and between discs 25 and 27 for transmitting the rotary torque generated by said 4 GB 2 111 320 A 4 electric motor drive assembly to the toolholder shaft 29.

10. The handplece of claim 9, wherein the discs 34 and 36 mounted on shafts 23 and 32, respectively, are arranged to each other under an angle.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1983. Published by the Patent office. 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained 1 i 1